The present invention relates to intermediates in the purification of cefdinir, i.e. 7-(Z)-[2-(2-acinothiazol)-4-yl)-2-hydroxyiminoacetamido]-3-vinyl-3-cephem4-carboxylic acid of formula 
Cefdinir may be used, e.g. in form of a monohydrate, as a pharmaceutical, e.g. antibiotic; see e.g. Y. Inamoto, Toshiyuki Chiba, Toshiaki Kiamimura und Takao Takaya, J. Antibiotics Vol XLI, No 6, 829, (1988).
Cefdinir may be obtained in impure form according to known production processes. It was now surprisingly found that impure cefdinir may be purified via the formation of a salt, e.g. in crystalline form, thereof.
In one aspect the present invention provides a compound of formula I in the form of a salt, e.g. crystalline, with dicyclohexylamine.
A compound of formula I in the form of a salt with dicyclohexylamine may be produced as follows:
Cefdinir, e.g. in the form of a solvate, such as a hydrate, e.g. in impure form, e.g. as obtained in a production process of cefdinir, such as a mixture of cefdinir and impurities, e.g. such as a mixture of by-products originating from the production process of cefdinir and cefdinir; may be treated in the presence of a solvent, e.g. in dissolved or suspended form, with dicyclohexylamine. A solvent includes any solvent which is inert towards cefdinir or towards cefdinir in the form of a salt with dicyclohexylamine, e.g. a polar organic solvent, such as amides, e.g. dimethylformamide; alcohols, e.g. methanol or ethanol; ketones, e.g acetone; e.g. in combination with water and water. A solvent system, e.g. mixtures of individual solvents, e.g. as described above may be used. A preferred solvent system may be e.g. acetone/water, including e.g. a ratio of about 100:1 such as 50:1, e.g. 20:1 to 1:5; such as 10:1 to 1:3, e.g. 5:1 to 2:1, e.g. about 1:1. Per equivalent of cefdinir about one equivalent or more, such as 5; e.g. 3, such as 2 equivalents of dicyclohexylamnine may be used, e.g. combined with the mixture of impure cefdinir in a solvent. A compound of formula I in the form of a salt with dicyclohexylamnine may crystallize e.g. from a reaction solution, or, e.g. a suspension of a compound of formula I in a solvent may be converted into a crystal suspension of a compound of formula I in the form of a salt with dicyclohexylamine. An anti-solvent may be added to the reaction mixture, e.g. in order to complete crystallization. An anti-solvent includes solvents wherein a compound of formula I in the form of a salt with dicyclohexylamine is insoluble or soluble only to a small extent if added to the solution or suspension of a compound of formula I in the form of a dicyclohexylamine, e.g. A polar solvents; e.g. ethers, such as diethylether, tetrahydrofurane; or a ketone, e.g. acetone. A compound of formula I in the form of a salt with dicyclohexylamine may be isolated from the reaction mixture, e.g. as conventional, e.g. by filtration, centrifugation.
A compound of formula I in the form of a salt with dicyclohexylamnine may be obtained in pure f form, e.g. in 98% purity and more, such as 99% to 100% purity; e.g. the amount of impurities present in cefdinir in impure form used for salt formation may be decreased; e.g. impurities of 10% and more in cefdinir in impure form may be decreased to impurities of 1 % and less, e.g. 0 to 1% in cefdinir in the form of a salt with dicyclohexylamine.
A compound of formula I in the form of a salt with dicyclohexylamine may be further purified by re-suspension or re-dissolution as described above, e.g. in an (anti) solvent (system), e.g. as described above.
In another aspect the present invention provides a process for the production of a compound of formula I in the form of a salt with dicyclohexylamrine, e.g. in crystalline form, comprising treating a compound of formula I, e.g. in form of a solvate, such as a hydrate, in a solvent with dicyclohexylamine and isolating a compound of formula I in the form of a salt with dicyclohexylamine, e.g. in crystalline form.
Cefdinir in free form, e.g. in the form of a solvate, such as a hydrate, e.g. monohydrate and in purified form, e.g. in respect with impure cefdinir used for the formation of a salt of a compound of formula I with dicyclohexylarnine, may be obtained from a compound of formula I in the form of a salt with dicyclohexylamine, e.g. as conventional for setting free a compound which is in the form of a salt, e.g. in the form of an amine salt; e.g. by adjusting an appropriate pH, e.g. 1.5 to 4, such as 2 to 3; of a mixture, e.g. a solution, of cefdinir in the form of a salt with dicyclohexylamine with a solvent, e.g. in the presence of water, preferably in water, e.g. by addition of an acidic agent, such as an organic or inorganic acid, preferably an inorganic acid, e.g. sulphuric acid. Cefdinir, e.g. in the form of hydrate, e.g. monohydrate may crystallize and may be isolated, e.g. as conventional, e.g. by filtration, centrifugation. A compound of formula I may be obtained according to the process of the present invention as such or in the form of a solvate, e.g. a hydrate, e.g. a monohydrate. A compound of formula I obtained according to the process of the present invention as such may be converted into a compound of formula I in the form of a solvate, e.g. a hydrate, such as a monohydrate and vice versa.
In another aspect the present invention provides a process for the production of a compound of formula I, e.g. in form of a solvate, such as a hydrate, eg. monohydrate comprising converting a compound of formula in the form of a salt with dicyclohexylamine, e.g. in crystalline form, into a compound of formula I, e.g. in the form of a solvate, and isolating a compound of formula I, e.g. in the form of a solvate.
In another aspect the present invention provides a process for the purification of cefdinir in a mixture of a compound of formula I with impurities, comprising forming a salt of a compound of formula I with dicyclohexylamine; and converting a compound of formula I in the form of a salt with dicyclohexylarine, e.g. in crystalline form, into a compound of formula I, e.g. in the form of a solvate, and isolating a compound of formula I, e.g. in the form of a solvate.
A compound of formula I in the form of a salt with dicyclohexylamine is useful in the purification of cefdinir in impure form.
In another aspect the present invention provides the use of a compound of formula I in the form of a salt with dicyclohexylarine, e.g. in crystalline form in the purification of a mixture of a compound of formula I with impurities.
The present invention has several surprising advantages:
A compound of formula I in the form of a salt with dicyclohexylamine may be in a crystalline form; cefdinir in the form of a salt may be obtained in surprising high purity, e.g. 98% purity and more, e.g. 98% to 100%; production of the salt is simple; cefdinir obtained from the salt may be surprisingly pure, e.g. 98% and more, e.g. 99% to 100%.
It is surprising that cefdinir under the basic conditions of the salt formation according to the present invention is stable, because from e.g. Yoshihiko Okamoto et al., J. of Pharmaceutical Sciences, Vol 8S, No 9, 976, (1996) it is known that cefdinir may be instable in a basic environment; it was e.g. found that cefdinir in the presence of other amines, e.g. tert.-octylamine under similar conditions may be, e.g. heavily, degraded.
In another aspect the present invention provides crystalline 7-(Z)-[2-(2-aminothiazol4-yl)-2-hydroxyiminoacetamido]-3-vinyl-3-cephem-4carboxylic acid/dicyclohexylammonium salt of formula 